Implantable cardiac defibrillators include patch defibrillators with a lead configured as a patch, which is attached to the surface of the heart or embedded in the patient subcutaneously. For example, one early patch lead included a rectangular patch that is applied around the patient's heart and is implanted by performing a thoracotomy on the patient. Other modifications or additions to the early patch designs were aimed at improved performance, improved patient tolerability, and simplified implanting. Despite improvements, patch leads typically suffer from a significant degree of crinkling, migration, erosion, and other problems related to the patch. Another drawback to patch leads is the need for surgery to implant the patch lead. This results in significant levels of operative mortality and infection of the patch, which can cause a life-threatening condition. Patch leads are undesirable because of these structural problems and risk of fatal complications.
Transvenous implanting of defibrillator leads was developed as an alternative to patch defibrillators. A transvenous lead including a defibrillator coil is typically inserted via the subclavian, internal jugular, or cephalic veins. Compared to the patch defibrillator leads, the transvenous leads show a reduction of operative mortality and are easier to implant. However, many transvenous systems require several coils in the right ventricle, the superior vena cava, the innominate vein, and sometimes even in the coronary sinus. This requires numerous leads all going in the same vein. This is undesirable because of consequences such as fibrosis or occlusion of the subclavian vein, obliteration of the superior vena cava, or simply mechanical obstruction of the vein. In addition, some of the transvenous systems require placement of a patch on the chest wall to render them effective. Using a patch results in all of the potential problems of patch leads and removes many of the advantages of the transvenous lead.
Although using transvenous leads reduced mortality and the number of complications, compared to patch leads, significant problems still occurred. One major problem is that transvenous leads migrate within the patient. Removal of a transvenous lead can also be a severe problem. Some of patients receiving transvenous leads are transplant candidates who receive a transvenous defibrillator system as a temporary measure, while awaiting transplant, to prevent sudden death from arrhythmia. In this case removal may not be a problem if the lead is removed soon after implantation. However, most of the transvenous leads having been in place for several weeks or months are extremely difficult to remove to allow the implant of the donor heart.
Because an intravenous lead that has been implanted for a long time is extremely difficult to remove, they can create problems if they fail. For example, there may not be room in the vein for additional leads. Overall, removing a transvenous lead requires a risky and difficult operative procedure. Frequently, removal requires cardiopulmonary bypass.
Transvenous defibrillator leads also cause other significant complications. For example, a transvenous lead can result in thrombosis of the subclavian or innominate veins, a complication which is usually irreversible. Severe fibrosis of the leads on the endocardial surface of the heart also occurs. This increases the defibrillation thresholds and makes removal of the leads impossible. Other complications include dislodgement, right ventricular perforation, creation of ventricular septal defect, infection, right atrial thrombus formation, subclavian vein thrombosis, pulmonary embolism, insulation breakage, development of a crush or compression fracture of the leads, and embolization of the distal lead.
Problems related to the use of transvenous leads increase health care costs. Complications of transvenous leads result in hospital readmissions, operative lead revisions, lead replacement, and lead failures. The so-called lead crush syndrome, which is the pinching of the transvenous leads at the thoracic inlet between the clavicle and the first rib is a very well known problem, not only with defibrillators, but pacemaker systems as well. The problem of chronic subclavian vein obstruction is not a mild one and some of those patients cannot be treated, even surgically, to reestablish the patency of the vessels.
Many patients are not candidates for receiving a transvenous defibrillator. For example, patients who have had either previous transvenous systems and have developed fibrosis and/or occlusion of the subclavian vein are not candidates for further transvenous leads. Some patients develop obliteration of the superior vena cava due to multiple leads previously placed. Some patients with transvenous pacemakers of the bipolar type, which include two leads in addition to the lead used for the defibrillator, do not have room for additional leads. The innominate, subclavian, and superior vena cava veins do not have limitless capacity to take so much hardware. Other patients, such as children, simply are not candidates for transvenous defibrillator systems. Although not a large population, there are children who require defibrillator therapy and are unable to receive it because of a lack of a proper device, either of the transvenous or patch designs.
To overcome these limitations and avoid these problems, a new simple epicardial implantable defibrillator lead was developed.